The proper use of potassium fertilizer can stimulate a significant yield increase. However, the application of excessively high rates of potassium can reduce the availability of soil calcium for apple trees. The potassium fertigation rate must meet the apple tree’s requirements so that the applied fertilizers can be absorbed by the roots as much as possible. Crop load in apple orchards sometimes varies significantly in different years. The potassium content in apple fruits is relatively high, and the maximum requirement for this nutrient occurs when fruits grow and ripen. Different crop loads at that time mean the various demands of trees and need for changing application rates for this nutrient. The investigation was carried out in the experimental orchard of I.V. Michurin Federal Scientific Centre (Michurinsk, Russia) in 2016 and 2017 (52.885131, 40.465613). We studied seasonal changes of potassium and calcium contents in soil, fruits, and leaves and their relationship with yield during the research. We paid much attention to the potassium rate shift on its content in leaves and fruits and cultivars “Lobo” and “Zhigulevskoye” yield. If the potassium application rate changes according to the actual crop load, it stimulates the yield growth or (if the crop load was relatively low) the reduction of the rate did not lower the productivity. Moreover, we studied the relationship between potassium and calcium nutrition. The decrease in potassium fertigation rate increased the availability of soil calcium. It was the reason for fruit calcium concentration enlargement and mitigation of the K/Ca ratio. We also specified some parameters for soil–leaf diagnosis for potassium nutrition during the growing season.
Our work aimed to study the effectiveness of the combined use of various foliar fertilizers and protection products in tank mixtures for the scab suppression and their impact on productivity. The studies were carried out under the conditions of experimental plantations of the I.V. Michurin Federal Scientific Center according to generally accepted methods. We determined the biological effectiveness of the plant protection systems used, the formation of productivity components (fruit set, average fruit weight and yield per tree), the content of the main nutrients in the soil, leaves, and fruits. The application of a conventional plant protection system has contributed to better protection of apple trees from scab. The ecologized system has also provided a sufficiently high level of protection, which allows recommending it to producers. The introduction of ecologized protection systems that reduce the pesticide pollution of the environment requires various support measures for producers. The use of an ecologized system of foliar nutrition provided an increase in plant protection effectiveness, especially when combined with regular soil fertilizer application, as well as in optimizing the mineral composition of fruits. Biologization of soil nutrition is one of the most critical tasks for preserving soil fertility in intensive horticulture. The soil application of bacterial fertilizers contributed to a significant increase in productivity. The highest results were obtained when applying biological fertilizers together with reduced rates of mineral fertilizers.
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